Secondary endpoints will compare changes in sickle cell disease related events (pulmonary hypertension, cerebrovascular events, renal function, avascular necrosis, leg ulcer) and functional outcomes [6-minute walk distance (6MWD), health-related quality of life, cardiac function, pulmonary function, and mean pain intensity as assessed by a multidimensional electronic pain diary] from baseline to 2-years after assignment to treatment arms.